1. Field of the Invention
The present invention relates generally to a safety device for a rotary press, and more particularly to a safety device for guarding a roller nip in a sheet-fed rotary press.
2. Description of the Background Art
A safety device for guarding a roller nip in a sheet-fed rotary press is disclosed in West German patent No. 2,914,152. The safety device includes two separate guard plates that are pivotally interconnected by a hinge. A first one of the guard plates is disposed at the roller nip from which the fed sheet issues. When the safety device is in its "normal" position used during printing, both of the guard plates serve as a sheet guide, and the first guard plate is pivoted out of its guard or safety position at the roller nip. This ensures that the trailing end of the printed sheet is not smeared on the edge of the first guard plate during continuous printing which could occur when the rotary press is fed with heavy sheets or board which tend to "set-off" from the impression cylinder. To wash the impression cylinder, the first guard plate is moved into its safety position by first moving the second guard plate away from the roller nip to give access to the impression cylinder. When this is done a lever operates a switch to prevent the printing press from being started. A disadvantage with this particular safety device is that the "inching" drive to the printing press is not stopped electrically when the first guard plate at the roller nip is contacted, which presents a safety hazard when the impression cylinder is washed by hand. Also in the safety position the press drive can operate only in a "backwards" inching mode since during the washing of the impression cylinder a second roller nip in the printing unit is exposed and would tend to grab a person's hand if the press drive were operated in a "forward" inching mode. During washing of the impression cylinder, the second roller nip becomes exposed because the second guard plate must be moved from the second roller nip to give access to the impression cylinder.
Many other devices for guarding the entry of the roller nip are known, for example, from West German patent Nos. 766,210; 1,165,044; 1,561,070; and 1,611,238; and French patent Nos. 833,280; and 1,579,086. These safety devices secure the entry side of a roller nip when the press stops, when the safety device is contacted or when access to the roller nip is reduced or impeded by resilient plates acting oppositely to the entry direction. However, unsmeared printing sheets cannot always be delivered from the exit of the roller nip since the guards cannot be pivoted out of the path of the sheet during printing as well as pivoted by the operator during servicing or adjustment.